Copying originals onto both sides of a receiving sheet is generally known. See U.S. Pat. No. 4,453,819 and Research Disclosure February 1980, No. 190, page 61, No. 19015. See also Japan A-5977451 and U.S. Pat. Mo. 4,209,249 in which images of all even numbered originals are applied to one side of receiving sheets in a first cycle, the receiving sheets are stored in a stack and then images of all odd numbered originals are applied to the other side of the receiving sheets in a second cycle In Disclosure 19015 a circulating path having space for two sheets is disclosed.
In U.S. Pat. No. 4,453,819 a copying machine for copying at least one group of four originals in order on both sides of receiving sheets is shown. It comprises an imaging device for forming a transferable image on an image support, a fixed location consisting of an image transfer station for transferring the transferable image to a receiving sheet, first conveyor means for conveying receiving sheets through the image-transfer station and a circulating path with second conveyor means and a turnover device in which receiving sheets after passing the image-transfer station are turned over so that the receiving sheets can be conveyed through the image-transfer station in the turned-over position, the circulating path having a length sufficient to receive a number of receiving sheets.
In the method and a copying machine of this kind as described therein a number of receiving sheets equal to or smaller than the maximum number of receiving sheets that the circulating path can hold is brought into the circulating path after images have been formed on one side thereof.
During a first cycle a number of odd-numbered pages of a group of originals is copied and in a second cycle a number of even-numbered pages of this group of originals is copied, the numbers being equal to or less than the maximum number of receiving sheets that the circulating path can hold. The odd-numbered pages and the even-numbered pages may be numbered in sequence or identically.
If the odd and even pages are copied in numerical order, respectively, in two cycles, the circulating path will not be completely filled if the group of originals comprises less pages than the maximum number of receiving sheets that the circulating path can hold. Even if the same odd page and the same even page are copied a number of times respectively in the two cycles, the circulating path will not be completely filled if the number of times that the group of originals is to be copied is to be less than the maximum number of receiving sheets that the circulating path can hold.
If a plurality of pages sizes is used the length of the circulating path will generally have to be equal to or greater than the length of the longest receiving sheet that is to be printed on both sides as considered in the direction of passage In practice, this length may be many times greater than the length of the standard receiving sheets normally used in copying. The term "standard receiving sheets" in this context denotes the smallest size customary for the copying machine used with the method.
In the above known method, the circulating path is much longer than the length of receiving sheets normally used and the receiving sheets are taken through the circulating path at an accelerated speed. The acceleration increases as number of receiving sheets filling circulating path decreases. Such acceleration is a source of conveying malfunctions in the circulating path. Of course, this also applies to the deceleration of a receiving sheet in the circulating path following the acceleration.
Accordingly, it is an object of the present invention to provide a method and a copying machine of the kind referred to above wherein it is possible to carry out a high diversity of copying tasks, including tasks in which a small group of originals is required to be copied on both sides a large number of times, and tasks in which a large group of originals is to be copied on both sides a small number of times, without any loss of time and with little risk of malfunction occurring in the conveyance of receiving sheets in the circulating path.